Estimate how old a living tree is without cutting it down. Measure around the trunk 4.5 ft (1.37 m) above the ground, choose the species and get its approximate age using the forestry growth-factor method.
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What did you measure at 4.5 ft (1.37 m)?
Wrap a tape measure around the trunk 4.5 ft above the ground.
Years per inch of diameter. Fast growers 2-3, average 4-5, slow growers 6-8.
Growth factors describe forest-grown trees; open-grown trees often grow faster.
Enter your values to see the result.
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How to use the Tree Age Calculator
Measure the trunk 4.5 ft (1.37 m) above the ground on the uphill side, wrapping a tape measure around it.
Enter the measurement and choose whether it is the circumference or the diameter, and the units.
Pick the species, or enter a growth factor for a tree not on the list.
Adjust for conditions if the tree grew in the open or in a crowded forest.
Read the estimated age, and compare species in the table if you're unsure of the tree.
Tree age formula
Diameter (DBH) = circumference ÷ π, then estimated age = DBH (inches) × growth factor.
Example: a sugar maple measures 75 in around at 4.5 ft. DBH = 75 ÷ 3.1416 = 23.9 in, and 23.9 × 5.5 = about 131 years. Working in centimeters, divide by 2.54 first: 190 cm around = 74.8 in.
Growth factors and ages by circumference
Species
Growth factor
Age at 30 in around
at 60 in
at 100 in
Cottonwood
2.0
19
38
64
Quaking aspen
2.0
19
38
64
Silver maple
3.0
29
57
95
Pin oak
3.0
29
57
95
American basswood (linden)
3.0
29
57
95
River birch
3.5
33
67
111
Scotch pine
3.5
33
67
111
Green ash
4.0
38
76
127
Red oak
4.0
38
76
127
American elm
4.0
38
76
127
Red maple
4.5
43
86
143
Norway maple
4.5
43
86
143
Black walnut
4.5
43
86
143
Austrian pine
4.5
43
86
143
Colorado blue spruce
4.5
43
86
143
White (paper) birch
5.0
48
95
159
Black cherry
5.0
48
95
159
White oak
5.0
48
95
159
Douglas fir
5.0
48
95
159
Eastern white pine
5.0
48
95
159
Norway spruce
5.0
48
95
159
Sugar maple
5.5
53
105
175
Ironwood
7.0
67
134
223
Redbud
7.0
67
134
223
Dogwood
7.0
67
134
223
Shagbark hickory
7.5
72
143
239
Growth factors are the widely used values published by arborist and arboretum sources for trees in typical forest conditions in North America. They are estimates: a tree in rich, moist soil and full sun can grow much faster, while one in poor, dry or crowded conditions grows slower. For an exact age, count annual rings on a stump or an increment-borer core.
Frequently asked questions
How do I estimate a tree's age without cutting it?
Measure the circumference 4.5 ft above the ground, divide by π (3.14) to get the diameter, then multiply by the species growth factor. A red oak 60 in around has a 19.1 in diameter; 19.1 × 4.0 ≈ 76 years.
What is a tree growth factor?
It is the average number of years a species takes to add one inch of trunk diameter. Fast-growing trees such as cottonwood and aspen have a factor of about 2, most maples and oaks 3-5.5, and slow growers like dogwood, redbud and shagbark hickory 7-7.5.
Why measure at 4.5 feet?
4.5 ft (1.37 m) is "breast height", the standard foresters use for diameter at breast height (DBH). It avoids the flare at the base of the trunk. On a slope measure from the uphill side; if the trunk forks below 4.5 ft, measure just below the fork.
How accurate is the growth-factor method?
It is a rough estimate, often within about 20-25% for forest-grown trees. Soil, water, sunlight, competition and climate change growth rates a lot. Counting rings on a core sample taken with an increment borer is far more accurate.
Do yard trees grow faster than forest trees?
Usually yes. Open-grown trees with full sun and little competition often add diameter faster than the forest trees the growth factors were based on, so the method can overestimate their age. Choose "Open, ideal" to reduce the estimate by about 15%.
How do I convert circumference to diameter?
Diameter = circumference ÷ π. For example, 94 in around ÷ 3.1416 = 30 in diameter, and 150 cm around ÷ 3.1416 = 47.7 cm (18.8 in).
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